The Branched Feeding Tentacles of Dendrochirotid Sea Cucumbers

I recently posted this photograph on the “ID Please (Marine Creature Identification)” Facebook page, asking “Are these sea cucumber tentacles? Taken at Port Stanvac, South Australia.”

I soon received a reply from Frédéric Ducarme saying “Yes, dendrochirotid sea cucumbers.” Frederic provided me with a link to Wikipedia where it read ““Dendrochirotida are an order of sea cucumbers. Members of this order have branched tentacles and are suspension feeders. Examples include Thyonella and Cucumaria.”

The Wikipedia page went on to say, “Holothurians in this order are characterised by ten to thirty much branched tentacles which are sometimes digitate. They also have ring structures composed of ten calcareous plates circling the pharynx. They have both retractor and introvert muscles which means they can retract the tentacles into the mouth when not feeding. The body wall is either firm with large ossicles or of a soft consistency with few ossicles. In some genera, the animals attach themselves to hard surfaces but in others they burrow into soft sediments. Prey is captured by the sticky tentacles and transferred to the mouth.”

My photo had been taken during a survey dive at Port Stanvac on 5th December 2009. Here is another photo that I was able to take at the time: –

Sand sea cucumber tentacles

The Wikipedia page gave the following scientific classification details for Dendrochirotida: –

Phylum: Echinodermata

Class: Holothuroidea

Subclass: Dendrochirotacea

Order: Dendrochirotida

The page also went on to give details of the taxonomy for Dendrochirotida, as follows: –

Order: Dendrochirotida: –

family Cucumariidae (Ludwig, 1894)

family Cucumellidae (Thandar & Arumugam, 2011)

family Heterothyonidae (Pawson, 1970)

family Paracucumidae (Pawson & Fell, 1965)

family Phyllophoridae (Östergren, 1907)

family Placothuriidae (Pawson & Fell, 1965)

family Psolidae (Burmeister, 1837)

family Rhopalodinidae (Théel, 1886)

family Sclerodactylidae (Panning, 1949)

family Vaneyellidae (Pawson & Fell, 1965)

family Ypsilothuriidae (Heding, 1942)

I found a similar photo to mine in the “Critter ID” column by David Mullins in the July 2017 issue of Dive Log Australasia. It was on page 13 and it had been submitted by a Cory T, saying, “I shot what I thought was a type of hydroid – very feathery. When I moved in a little closer for another shot it quickly disappeared into the sand.”

David Mullins’ response was, “This is the “feeding tree” of a sea cucumber. Family Phyllophoridae, Neothyonidium sp.” He went on to say, “While we are all familiar with the sea cucumbers that look …. like cucumbers, feeding on the surface of the substrate, what are less well known are those that live in a hole in the substrate and feed by poking their greatly enlarged tentacles up and out but can completely withdraw if threatened. These are passive feeders on phytoplankton. The drifting particles are trapped in a mucus layer coating the arms. The arm is deflated and inserted into the mouth that over it and removes the particles as the arm is drawn back out. A fresh layer of mucus is applied at the mouth as there are no glandular cells for this on the arms. The arm is reinflated and another of the arms cycles through the process. If their feeding location is fruitful they may remain in the same location for the duration of their life.”

There is a photo of the tentacles of a “Large Burrowing Sea Cucumber”, Neothyonidium magnum on page 61 of Neville Coleman’s book titled “Sea Stars of Australasia and their relatives”. There is a photo of the tentacles of Thyone okeni on page 263 of Karen Gowlett-Holmes’ book titled “A field guide to the marine invertebrates of South Australia”. There is a photo of the tentacles of a Neothyonidium species on Plate 31.6 of “Marine Invertebrates of Southern Australia – Part I”.

According to the latter book, “The species in the order Dendrochirotida are benthic suspension feeders, passing food to the mouth by the tentacles. The other orders are deposit feeders, ingesting organic matter with mud or sand.”

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Steve Reynolds is the current President of MLSSA and is a long-standing member of the Society. Steve is a keen diver, underwater explorer, photographer and is chief author of the Society's extensive back catalogue of newsletters and journals.